Thermographically useful light sensitive image-yielding material containing finely divided sulfur particles



United States Patent .THERMOGRAPHICALLY USEFUL LIGHT SENSI- TIVEIMAGE-YIELDING MATERIAL CONTAIN- ING FINELY DIVIDED SULFUR PARTICLESToshimi Kishida, Masaaki Yoshioka, and Isamu Fushiki, Tokyo, Japan,assignors to Konishiroku Photo Industry Co., Ltd., Tokyo, Japan NoDrawing. Filed Aug. 2, 1966, Ser. No. 569,600 Int. Cl. G03c 5/54 US. C].96-29 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to athermographically useful image-yielding material comprising a supportand a photographic silver image-forming layer coated thereon, said layeror its photographically contiguous layer having finely divided sulfurincorporated therein. The object of the present invention is to providea new and useful material which, after formation of a photographic imagethereon, can be used as a mother sheet for thermographic process toobtain a large number of copies.

For the purpose of obtaining reproductions from such originals ashand-written documents, printed matters, and the like, various methodshave conventionally been developed. Of these, the thermographic processwhich We invented by utilizing the supercooling phenomenon (cf. JapanPrinter, vol. 47, No. 4, page 12 (1964)) is a novel process having manycharacteristics. By the present invention, it is intended to make saidprocess more advantageous by provision of a new and usefulimage-yielding material. Since the above-mentioned supercooling processis one of the thermographic type, it usually has failed to give clearreproductions of portions less in IR-absorbing nature. In contrastthereto, the image-yielding material of the present invention yields animage by utilization of silver photographic process and hence canprovide a clear copy regardless of the color of the original employed,which copy serves as a mother sheet for thermographic process to producea great number of copies. Further, the supercooling process is usefulonly in contact printing, whereas use of the material of the presentinvention makes it possible to obtain, by application of a photographicprocess, reproductions enlarged or reduced in size. Further, when thematerial of the present invention is used, any original which isentirely opaque and which is so thick, large or heavy as not to beaccepted by a usual copying machine can be reproduced with case.

In accordance with the present invention, there is provided athermographically useful image-yielding material which comprises asupport and a photographic silver image-forming layer coated thereon,said layer or its photographically contiguous layer having finelydivided sulfur incorporated therein. In one embodiment of the presentinvention, fine particles of sulfur may exist in the photographic silverimage-forming layer of the imageyielding material. In another embodimentof the present invention, they may exist in a protective layer, forexam- 3,522,047. Patented July 28, 1970 ple, coated on the photographicsilver image-forming layer, with or without an inter layer. Thus, it isto be understood that the term, photographically contiguous layerreferred to therein to mean a layer adjacent to the photographic silverimage-forming layer, regardless of the existence of an interlayertherebetween. Typically the above-referred photographic silverimage-formin layer is a light-sensitive photographic silver halideemulsion layer or a silver diffusion transfer-receiving layer. Theabovereferred photographic contiguous layer is a protective layer wellknown in the photographic art.

The invention will be illustrated in more full detail below. As statedbefore, the material of the present invention has a silver-imageyielding layer and if desired, a layer photographically contiguoustherewith, either one of these layers having finely divided sulfurincorporated therein, said sulfur being recognized as one ofheat-sensitive substances usable in the supercooling process. Asheat-sensitive substances in the supercooling process, many substanceshave been known in addition to sulfur. In the present invention, whereinthe silver photographic process is utilized, those giving detrimentaleffects to light-sensitive emulsions or diffusion transferimagereceiving materials are not usable. Further, in the presentinvention which requires such photographic treatments as development andfixation, water-soluble heat-sensitive substances also are not usablebecause they flow out during the treatments. For example, benzotriazolehas been a heat-sensitive material and has frequently been used in thesupercooling process. However, said material causes markeddesensitization on the light-sensitive photographic emulsions and henceis not suitable for the object of the present invention. Further,p-toluenesulfonamide is so high in water solubility that it flows out ofthe layer during the photographic treatments and hence is neithersuitable as the heat-sensitive substance of the present invention. Incontrast thereto, sulfur employed in the present invention, which isentirely insoluble in water, does not flow out during the treatments andit does cause neither fogging nor desensitization of photographicsensitive emulsions. Therefore, it is entirely suitable as aheatsensitive component of the image-yielding material of the presentinvention. Moreover, sulfur has many such advantages that it isexcellent in transferability, is long in supercooled state to make itpossible to obtain a stable dustadherable latent image, and can beincorporated in a relatively large amount into the layer, whereby agreat number of reproductions can be obtained from a single mothersheet. Commercial availability and cheap price of sulfur are additionaladvantages. In the art, the existence of sulfur in a photographicemulsion has been considered as causing a serious problem inphotographic properties. Taking this into account, the present inventionis unexpectedly beyond the prejudice of the prior art.

Any of the conventionally known light-sensitive photographic silverhalide emulsions can be successfully used for the preparation of aphotographic silver image-forming layer in the present invention.Further, any emulsions which are used to form an image-receiving layerof the silver diffusion transfer process can be used in the presentinvention, said emulsions being referred to image-receiving emulsionshereinafter. The above-mentioned lightsensitive silver halide emulsionsinclude not only the ordinary light-sensitive emulsions but also theso-called directpositive, light-sensitive emulsions which can directlygive positive image by utilizing the solarization phenomenon or Harscheleffect. Quick processable emulsions for stabilization method orheat-developable emulsions are also usable. These light-sensitiveemulsions may be treated, before use, by color sensitization, noblemetal sensitization or reductive sensitization, or by addition of suchadditives as stabilizers, hardeners and development-controlling agents.The image-receiving emulsion of the silver diffusion transfer process,which is suitable for the purpose of the present invention, is adispersion of colloidal noble metal or metal sulfide assilver-precipitating nuclei in a layer-forming binder as a protectivecolloid.

Now, how to use the material of the present invention will beillustrated below with reference to the case Where a light-sensitivedirect-positive photographic emulsion is used. In the first place, thematerial of the present invention is exposed through an image-bearingoriginal at desired magnification and then subjected to photographictreatments such as development and fixation according to the knownprocedures, whereby a mirror silver image is formed on the material ofthe present invention. In the second place, the material which is nowusable as a mother sheet is placed on a paper as receptor sheet and thenthe resulting composite is subjected to infrared irradiation, wherebysulfur of the image portion is transferred onto the paper, due to theaction of heat of the infrared-absorbing silver image portion, to yieldon the paper a latent image of sulfur in a supercooled state. In thethird place, the latent image yielded on the paper is developed bysprinkling thereon such a fine coloring powder as is ordinarily used inelectrophotographic process (hereinafter referred to as a toner). Thedeveloped image can be fixed by application of a solvent vapor, therebyto obtain a copy bearing a right image of the original. The infraredirradiation and image transfer can be effected repeatedly up to amaximum of about 200 times, whereby a large number of reproductions areobtainable from a single mother sheet.

In the present invention, the conventionally known silver halidephotographic process is utilized for the formation of images, andtherefore it is possible to obtain, according to desired objects,materials having any desired sensitiveness within a markedly wide range.Further, by application of many known techniques, such as colorsensitization, direct reversal and the like, imageyielding materialsusable for various purposes can be obtained. Further, as the imageformed by use of the present material is composed of infrared-absorbingand thermally conductive silver metal particles, heat of the silverparticles is well transmitted to heat-sensitive sulfur particles,whereby reproductions bearing clear images can be obtained with highetficiency by application of thermography.

The preparation of the image-yielding material of the present inventioncan be made as follows: Sulfur is conveniently prepared as a dispersionof fine particles, which dispersion is then mixed with a light-sensitivephotographic emulsion or the like. That is, sulfur is added to asolution prepared by first forming a solution of hydrophilic highmolecular weight dispersion medium and then adding thereto a suitablesurface active agent, and the resulting mixture is subjected to adispersing machine such as a ball mill to form a dispersion of finelydivided sulfur having a particle size of less than 50g, preferably lessthan g. As the high molecular weight dispersion medium, gelatine ispreferred, in general. In addition thereto, gum arabic, polyvinylalcohol, carboxy-methyl cellulose and sodium alginate also are usable.As the dispersion agent, alkylnaphthalenesulfonic acid, an alkylphenolethylene oxide polycondensate or saponin may be used. It is ofimportance that sulfur contains no such impurities as to injurephotographic properties, and may be in any form of crystalline sulfur orsublimated sulfur so far as it is pure. The thus obtained sulfurdispersion is mixed with a light-sensitive photographic emulsion or thelike, and the mixture is applied onto a suitable support and is thendried to obtain the image-yielding material of the present invention. Inthis case, if the amount of sulfur incorporated is excessively large,the sensitivity of the light-sensitive emulsion is damaged due to thediffusion of light, whereas if the amount is excessively small, noeffect can be attained. Generally, sulfur is preferably used in anamount substantially equal to the weight of silver halide in thelight-sensitive emulsion, but the amount may be suitably varied, withinthe range of from 0.0 5 to 5 parts per part of silver halide. That is, acommercially available photographic paper contains 2 to 3 g. of silverper square meter, and therefore sulfur may be used in an amount withinthe range of 0.1 to 15 g. As the support, paper is used, in general. Theimageyielding material of the present invention is to be subjected laterto thermographic process, and therefore the use of a thin paperfavorable in infrared transmission is preferred. However, there are somecases where a thin paper is used as a receptor sheet in thermographicprocess. In such cases, therefore, an ordinary photographic raw papermay be used as the support. In addition to paper, a film base such ascellulose acetate or polyethylene terephthalate may also be used as thesupport.

The typical applications of the image-yielding material of the presentinvention will be explained below. The image-yielding material isexposed imagewise by utilizing the conventionally known photographictechnique. In this case, the exposure is desirably effected by use of anoptical system because, as the most common mode of practice, it isconvenient to form a mirror image on the imageyielding material.However, in case a thin paper is used as the receptor sheet and the copycan be seen from the back, such exposure as to give a right image, i.e.contact printing, is acceptable. The exposed image-yielding material isthen subjected to treatment by development and fixation, thereby toobtain a silver image. In this case, the material may be subjected toany of a quick treatment utilizing stabilization process, a heatdevelopment, or a tanning development followed by washing off of theunexposed portion with hot water. The tanning development isparticularly advantageous in that the subsequent thermographic processcan be effected simply, because sulfur as a heat-sensitive material doesnot exist in any other portion than the image portion. All theabove-mentioned procedures and operations are the photographictechniques known heretofore, and not much explanation thereof would benecessary.

The material, on which a silver image has been formed in the abovemanners, is then used as a mother sheet for the thermographic process toobtain a large number of reproductions. The thermographic process iscarried out by placing on the mother sheet an ordinary paper as areceptor sheet, subjecting the composite to IR-irradiation by which thesulfur in the image portion is transferred onto the receptor sheet toform a dustable latent image in a supercooled state, developing thelatent image with a toner and then fixing the image to obtain a copy.IR- irradiation of the composite of the mother sheet and transfer papermay be effected, by use of a strong infrared ray lamp, the silver imageportion on the more readily IR-transmissible side of the composite. Theabove procedure may be effected by use of a commercial thermographicmachine having a transparent quartz infrared ray lamp with an output of30400 w./cm. Typical of the thermographic machines of this kind areThermofax Secretary type copying machine (trade name; manufactured byMinnesota Mining & Manufacturing Co., U.S.A.). The mother sheetsubjected to tanning development contains no sulfur in any other portionthan the image portion, and therefore a composite thereof with areceptor sheet can be passed between hot rolls having a surfacetemperature of about 0, whereby a dustadhering latent image can besimply formed on the receptor sheet. The dust-adhering, supercooledlatent image formed on the receptor sheet in the above manner is thendeveloped by dusting with a toner. The toner is prepared byincorporating a coloring matter in a thermofusible or solventvapor-soluble resin and finely dividing the mixture. Any toner which isordinarily employed at present in the electrophotographic process can beused as such.

The-development may be conducted by utilization of any methodemployed inthe electrophotographic process, such as magnetic brushing method,cascade method or smoke chambermethod. In this toner is used a coloringmatter which is stable by itself, and therefore the resulting copy ismarkedly stable and does not suffer from fading. Further,- the toner canbe incorporated with a coloring matter or any color tone, it is possibleto obtain copies bearing not only black colored images but also imagescolored to optional colors. After completion of the toner development,the receptor sheet is treated by application of heatflor solvent vapor,whereby a copy with the fixed image 'is obtained. In the case of thematerial of the presentjinvention, a considerably large amount of sulfuras a. heat-sensitive material can be incorporated into the layer, andtherefore up to about 200 sheets of clear copies can be obtained from asingle mother sheet.

The image-yielding materials of the present invention utilizelight-sensitive photographic silver compounds for image formation andhence are variable in sensitivity over a wide range. Further, thepresent materials can be processed by many known techniques, e.g. directreversal, tanning development and the like. The present material cantherefore be utilized not only in the reproduction of hand-writtendocuments and printed matters but in a varietyof fields for copying andprinting. For example, letters .are directly printed on the material byuse of a photographic typesetting machine and the material is used as amother sheet to obtain a great number of copies, or an image of ameteorological radar is directly photographed and a plurality ofcopiesof the photograph are immediately prepared so that the copies maybe delivered to concerned sections. Further, the toners employed may bethose having optional color tones, and therefore it is possible toobtain a natural color" copy by preparing 3 mother sheets from atricoloranalyzed halftone negative, transferring the images of themother sheets onto one receptor sheet, and developing the images by useof cyan, yellow: and magenta toners, respectively.

following examples illustrate the present invention, but it should beconstrued that the invention is not limited thereto but variousmodifications are possible within the scope of the claimed invention. Inthe examples, all parts are expressed by volume.

EXAMPLE 1 150 g. of sublimated sulfur powder is added to a solution of 5g. of saponin in 1.1 of 1% aqueous gelatine. The resulted mixture istreated in a porcelain ball mill for 20 hours to form a homogeneoussulfur dispersion, which is then used for the preparation of two samplesA and B.

(A) 0.8 part of the sulfur dispersion is mixed with 1 part of agelatinous silver chlorobromide emulsion (gelatine cone. 3%). Theresulting mixture is coated on a thick tracing paper to dry thickness of5.5,u. and then dried.

(B) To 1 part of a gelatinous silver chlorobromide emulsion (gelatinecone. 3%) is added 0.8 part of 1% gelatine. The mixture is coated on athick tracing paper to dry thickness of 5.5p. and then dried. On thedried paper, the above-prepared sulfur dispersion is coated as aseparate layer to dry thickness .of 2.5;!

(C) To 1 part of a gelatinous silver chlorobromide emulsion (gelatinecone. 3%) is added 0.8 part of 1% gelatine. The mixture is coated on athick tracing paper to dry thickness of 5.5 1. and dried.

The above samples A and B are the image-yielding materials according tothe invention and the sample C is a control. Imagewise exposure is givento these samples which are then developed at 20 C. for one minute.Photographic properties of these samples are measured immediately aftertheir preparation and after their incubation for two days at 55 C. The.results are set forth below:

Specific speed Max. density Fog Incu- Ineu- Incu- Just bated Just batedJ 11st bated after for 2 after for 2 after for 2 prepadays at prepadaysat prepadays at Sample ration 55 C. ration 55 C. ration 55 C A 93 1.9 1. 8 0.01 0. 01. B. 94 94 1.6 1. 6 0.01 0.01 C (control)- 99 2. 1 2. 10. O1 0. C1

The above data shows that the image-yielding materials are stable duringtheir storage under considerably strict conditions and that theirphotographic properties are substantially free from the advsereinfluence of sulfur.

The samples A and B are employed to obtain copies i nthe followingmanners: A microlm negative bearing an original image is printed atdesired magnification onto the sample as an image-yielding material soas to obtain a mother sheet bearing a silver mirror image. On thesensitive side of said motor sheet is placed an ordinary paper as areceptor sheet, and the composite is subjected to infrared irradiationfro mthe back side of said mother sheet by means of a Thermographiccopying machine. The receptor sheet is removed from the mother sheet.The latent image thus formed on the receptor sheet is then developedaccording to the cascade method using Konifax Toner-PP (trade name,manufactured and sold by Konishiroku Photo Industry Co., Ltd.) andthermally fixed by use of Konifax fixing machine (trade name,manufactured and sold by Konishiroku Photo Industry Co., Ltd.) to obtaina clear copy. By repetition of the above thermal transfer dustdevelopment and fixing operations in sequence, 200 sheets of clearcopies could be obtained from one mother sheet.

EXAMPLE 2 50 mg. of colloidal silver sulfide is suspended in 1 l. of a3% aqueous gelatine solution. To the suspension is added 30 mg. ofphenyl mercaptotetrazole as a color modifier to form a solution for adiffusion transfer imagereceiving layer. The solution is mixed with 0.3l. of the sulfur dispersion employed in Example 1, and the mixture iscoated onto a thin photographic paper to a dry thickness of 2a and isthen dried to obtain an image-yielding material of the presentinvention. This material is employed to obtain copies in the followingmanners: A negative material for diffusion transfer is brought intocontact acording to the ordinary procedure with an original to bereproduced and the composite is exposed by reflection printing. Theexposed negative material is placed on the above-mentionedimage-yielding material, and the resulting composite is treatedaccording to a diffusion transfer method to form a silver image on theimage-yielding material which is now ready for use as a mother sheet.The silver image on said mother sheet is a right image, therefore in thethermal transfer thereof, a thin IR-transmissible transparent paper isused. Application of infrared irradiation is made onto the back side ofthe transfer paper. Thereafter, the same dust development and thermalfixation as in Example 1 are effected to obtain 100 sheets of copies.

What we claim is:

1. A method of producing thermographically at least one reproduction ofphotographable material from a master, which comprises the steps ofproviding a support bearing an emulsion of a light-sensitive silverimageforming layer containing finely divided sulfur of a particle sizeof less than 50 Ill/L in an amount of 0.05 to 5.0 g. per gram of silvercompound in said layer, photographic'ally exposing said image-forminglayer and developing and fixing the resultant image, providing areceptor sheet of material and placing said support now bearing saidimage in contact therewith, subjecting the resultant composite toinfrared radiation, whereby sulfur from the image-forming layer istransferred onto said receptor sheet to yield a latent image of sulfurthereon in a supercooled state and then developing and fixing saidlatent image.

2. A method of producing thermographically at least one reproduction ofphotographable material from a master which comprises the steps ofproviding a support bearing an emulsion of a light-sensitive silverimageforming layer and an outer light-transmitting layer containing from0.5-5.0 g. finely divided sulfur of a particle size of less than 50 mpper gram of silver compound in said layer, photographically exposingsaid image-forming layer and developing and fixing the resultant image,providing a receptor sheet of material and placing said support nowbearing said image in contact therewith, subjecting the resultantcomposite to infrared radiation, whereby sulfur from the image-forminglayer is transferred onto said receptor sheet to yield a latent image ofsulfur thereon in a supercooled state and then developing and fixingsaid latent image.

3. Thermographically useful image-yielding material which comprises asupport and a light-sensitive silver 8 image-forming layer coatedthereon and a light-transmitting outer layer containing from 0.5-5.0 g.finely divided sulfur of a particle size of less than mp per gram ofsilver compound in said layer.

4. Thermographically useful image-yielding material which comprises asupport and a light-sensitive silver image-forming layer coated thereon,said layer containing from 0.05 to 5.0 g. of finely divided sulfur of aparticle size of less than 50 mg per gram of silver compound in saidlayer.

References Cited UNITED STATES PATENTS 3,158,481 11/1964 Shanefield96-29 GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, AssistantExaminer US. Cl. X.R. 96-67; 250-

